I'm creating a fixed-format children's book in Sigil intended for all kindle devices plus iBooks later.
My manually created TOC works fine on Kindle Fire. On ordinary kindle, the links don't work, search isn't an option and link to TOC not functioning either.
Does fixed-format kill functions on older devices.
Kindle has been updated recently.
From Sigil, I use Kindle Previewer.

As an experiment, I used Calibre to create an AZW3. Link, search etc work, but it kills the fixed format.

Also, this needs to be sold on Amazon. So i need to sue acceptable format.

Use your word processor or graphics application to build your original file so you can make copies [One for Fire, one for Kindle 2 one for iPad etc] and change the page or screen size for each destination device. Then export as PDF. Kindles format is free-flowing like html. Expect your output to be ONLY for a landscape or portrait screen, hope that's not an issue for you?